In those days games with great graphics and sound values played like crap and had terrible design. DKC had the whole package, the graphics were a generational leap, the sound felt like CD quality, the gameplay was great and fast and the level design was great too.
I don't get people calling the gameplay mediocre, it's as good as Mario and Sonic and miles ahead the average platformer, maybe not as innovative as the graphics but certainly up there with the best.
It's just impossible to understand what it was like because the industry hasn't really evolved that much in decades, it's always just extra power, more polygons etc. But games just don't leap over what's before anymore like Doom, DKC, Mario 64 did. It was a time of great disruption.